#include<iostream>
using namespace std;
class Factory
{
    public:
    static int totalProduction;
    static bool add(int items)
    {
        if(items<0)
        {
            cout<<"Invalid input"<<endl;
            return false;
        }
        totalProduction+=items;
        return true;
    }
};
int Factory::totalProdution=0;
int main(){
    int n,val;
    if(!(cin>>n))return 0;
    for(int i=0;i<n;i++)
    {
        cin>>val;
        if(!Factory::add(val))return 0;
    }
    cout<<Factory::totalProduction<<endl;
    return 0;
}